The present invention relates generally to semiconductor devices and techniques for providing dummy fill structures beneath thin film resistors that preferably are symmetric with respect to the thin film resistors, so as to reduce self-heating, preferably uniformly, of the thin film resistors and improve the stability of the thin film resistors, especially the stability of ratios of resistances of thin film resistors having different current densities therein.
“Dummy fill” has been commonly utilized in conjunction with use of chemical mechanical polishing (CMP) in integrated circuit chip fabrication processes. Dummy fill also has been utilized beneath an array of thin film resistors to disperse laser beam energy reflected during trimming of the thin film resistors so as to reduce optical interference of reflected laser energy with the incident laser beam and thereby improve laser trimming of the thin film resistors, as described in commonly assigned U.S. Pat. No. 6,818,966 issued Nov. 16, 2004 to Beach et al. In CMP processes, it is necessary to have an adequate density of the materials being polished to avoid localized over-polishing, referred to as “dishing”, which results in a non-planar surface after the polishing. Non-planar surfaces are incompatible with many conventional integrated circuit processing steps. For example, if interconnect metallization is deposited on a non-planar surface and the resulting surface then is subjected to a CMP operation, there may be residues of undesired metallization which are not adequately removed. Such undesired metallization residues may cause electrical shorting or other problems that lower integrated circuit processing yield.
When CMD operations are performed in the vicinity of thin film resistors, the “dishing” referred to above may cause large “systematic” errors in the resistances and ratio-matching of resistances of the thin film resistors. This is because stress associated with the thin film resistive material, especially SiCr which is somewhat piezo-resistive, causes identical SiCr resistor segments to have slightly different resistances, due in part to the variation in piezo-resistivity. Not only is the resistance of every identical resistor or resistor segment different for different die and different wafers, the systematic error associated with the resistor segments typically varies significantly even within the same die.
For prior art integrated circuit surface planarizing processes, it was considered unacceptable to have any metal or any other abrupt integrated circuit topology features located underneath thin film resistors. This was because the prior art integrated circuit surface planarizing processes could not adequately planarize or precisely flatten such topology features well enough to avoid severe disruption of the matching and stability of the thin film resistors due to material stresses and/or discontinuities (especially in very thin layers such as SiCr which, for example, may be only about 30 Angstroms thick) and/or optical inaccuracies associated with photolithography techniques being used.
FIG. 5 shows an accurate section view of a portion of a prior art integrated circuit including a prior art thin film resistor structure in which a sichrome (SiCr) thin film resistor 2 is formed on a chemically and a mechanically polished surface of an “interlevel dielectrics” layer or region 21 which includes several conventional dielectric layers (not shown). Layer 21 is formed over a “pre-metal dielectrics” layer 18, which is formed on a silicon layer 16. Silicon layer 16 may be formed on a silicon wafer substrate. (The term “pre-metal dielectrics” is well-known in the integrated circuit industry, and refers to contiguous different pre-metal dielectric layers having somewhat different doping, including, for example, for example, boron-phosphorus “TEOS” (tetrethylorthosilicate) layers.) Thin film resistor “head” 22A may be composed of TiW (titanium-tungsten) which extends through an opening in a dielectric sub-layer of oxide region 20 to make electrical contact with the left end or head of SiCr resistor 2, and also makes contact with a portion 24A of a metallization layer 24A,B, typically formed of aluminum, formed on the upper surface of interlevel dielectric region 21. In a similar manner, a separate portion 24B of metallization layer 24A,B makes electrical contact to the right end or head of SiCr resistor 2. Interconnect “Metal 2” conductors 24A and 24B extend along the surface of dielectric layer 21 and are connected to electrodes of various circuit elements (not shown) such as transistors, capacitors, and resistors, and may also be connected by appropriate conductive vias to “Metal 1” conductors such as conductor 9.
Thus, there is an unmet need for an improved, inexpensive integrated circuit thin film resistor structure and method for reducing or eliminating inaccuracy in the resistances and ratios of the resistances of thin film resistors.
There also is an unmet need for an improved, inexpensive integrated circuit thin film resistor structure and method for reducing or eliminating inaccuracy in the ratios of resistances of thin film resistors having substantially different current densities therein.
There also is an unmet need for an improved, inexpensive integrated circuit thin film resistor structure and method for reducing self-heating of a thin film resistor and causing self-heating that does occur to be uniform.
There also is an unmet need for an improved, inexpensive integrated circuit thin film resistor structure and method for improving nucleation of resistive material being deposited on abraded dielectric surfaces.